Multi-line telephone communications system

Abstract

There is disclosed a multi-line telephone communications system where the need for the hundreds of conductors that are necessary to connect each station to the control and switching equipment is eliminated. This is achieved by replacing the status indicating leads with analog signals impressed upon the voice leads. A specific signal level is assigned to each of the ring, busy, idle and hold functions so that the voice leads carry both the audio signal and status information signal for each line selectable at the telephone station. In response to activation of the telephone keys by the user a cross point switch establishes a voice signal connection between a selected voice line and a talk path associated with the selecting telephone station. A status signal representative of the status of at least the connected voice line and distinct from voice signals is impressed upon the voice line. This status signal is detected and processed for activating the status indicators at each telephone station. Assignment of lines to particular keys of a telephone station is achieved by storing the assignment in a programmable memory. Whenever a line assignment is to be changed from one key to a different key, it is necessary only to enter the change by reprogramming the memory.

We claim: 
     
       1. In a multi-line key telephone system providing direct voice communication with selected telephone lines external to the system, the external lines being selectable by at least one telephone station, each station providing a talkpath and having line selecting keys and means for indicating the status of the selectable line, comprising: a voice line internal to the system, coupled to each of the respective external telephone lines;   crosspoint switch means adapted for installation at a location remote from the telephone stations for selectably establishing, in response to activation of the telephone keys by the user, a voice signal connection between a selected voice line and a talkpath associated with the selecting telephone station;   means for impressing upon said voice line a signal representative of the status of at least the connected voice lines, said status signal being distinct from voice signals carried by said talkpath; and   means responsive to said status signal for activating the indicating means of each such telephone station to indicate the status of the voice lines.   
     
     
       2. The multi-line telephone system set forth in claim 1, further comprising: control means including a programmable memory for storing indications of the voice lines assigned to the respective telephone station keys, said control means being responsive to telephone key actuation to generate a command to effect a corresponding crosspoint connection of said crosspoint switch means.   
     
     
       3. The multi-line telephone system set forth in claim 1, wherein: said crosspoint switch means comprises at least one solid state device having individually controllable electronic switches for effecting an electrical connection between each telephone station talkpath and a selected one of said voice line.   
     
     
       4. The multi-line telephone system set forth in claim 1, wherein said status signal is an analog signal and the means responsive to said status signal includes: an analog/digital converter;   means for individually connecting each of said status signals to said analog/digital converter to produce a corresponding digital status signal; and   means for transmitting said digital signal to said telephone station to activate the status indicating means for each of said voice lines.   
     
     
       5. The mutli-line telephone system of claim 4, comprising: means for interrogating the output of said analog/digital converter to sequentially transmit digital status data for individual voice lines.   
     
     
       6. The multi-line telephone system of claim 1, comprising: a data conductor coupling each telephone station with said crosspoint switch means for communicating digitally formatted switch control data therebetween independently of voice communication over said voice signal connection.   
     
     
       7. The multi-line telephone system of claim 1, wherein: each voice line comprises a pair of conductors, the direct current signal impressed thereon being in common mode relation to the voice signal carried thereby.   
     
     
       8. The mutli-line telephone system of claim 7, comprising: means for averaging the signals appearing on said voice line conductor pair and coupled to said analog/digital converter, thereby to cancel audio signal components from the coupled signal.   
     
     
       9. The multi-line telephone system of claim 1, wherein: said signal impressing means is effective to produce different preselected voltage levels indicative of different line status conditions.   
     
     
       10. The multi-line telephone system of claim 9, wherein: said different preselected voltage levels correspond to at least two to the ring, hold and busy status conditions of the associated voice line.   
     
     
       11. The multi-line telephone system set forth in claim 1, further comprising; diagnostic sampling means for detecting the status signals on selected ones of said talkpaths to thereby detect the connection status of the sampled talkpath.   
     
     
       12. The multi-line telephone system of claim 1, comprising: a ring signal detector responsive to a ring signal on an external line; and   means for isolating said ring signal from the corresponding voice line,   said signal impressing means being effective to impress an analog voltage level on said corresponding voice line representative of an incoming ring status.   
     
     
       13. The mutli-line telephone system of claim 1, wherein: the means responsive to said status signals includes means for signaling the telephone stations of the occurrence of an incoming call on the external line,   the system further including means responsive to a telephone pick up at a telephone station for generating a signal representative of a line-selected condition on the talkpath for such station,   the crosspoint switch means being responsive to said busy condition signal to close the crosspoint switch for interconnecting said talkpath and said corresponding voice line.   
     
     
       14. The multi-line telephone system of claim 13, further comprising: line termination means for indirectly coupling audio signals on the external line to an associated voice line while isolating any status signals from the external line, and   means for precluding audio coupling of said external line to said voice line except when a command to connect a talkpath to said voice line occurs.   
     
     
       15. The multi-line telephone system of claim 4, wherein: said connecting means sequentially routes said status signals for each voice line to said analog/digital converter,   the corresponding digital signals being transmitted sequentially for reception by said telephone station.   
     
     
       16. The multi-line telephone system of claim 15, further comprising: means for storing said digital signals prior to sequential transmission to said telephone status.   
     
     
       17. The multiline telephone system set forth in claim 1, further comprising: control means including a programmable memory for storing and reassigning indications of the voice lines assigned to the respective telephone station keys, said control means being responsive to telephone key actuation to generate a command to effect a corresponding crosspoint connection of said crosspoint switch means.   
     
     
       18. In a multi-line key telephone system providing direct voice communication with selected telephone lines external to the system, the external lines being selectable by at least one telephone station, each station providing a talkpath and having line selecting keys and means for indicating the status of the selectable line: a voice line internal to the system, coupled to each of the respective external telephone lines;   crosspoint switch means adapted for installation at a location remote from the telephone stations for selectably establishing, in response to activation of the telephone keys by the user, voice signal connections between selected voice lines and talkpaths associated with the selecting telephone stations;   means for impressing upon said voice lines signals representative of the status thereof, said status signals being distinct from voice signals carried by said talkpaths;   means responsive to said status signals for developing corresponding digital status signals;   a data conductor connected to said telephone station for serially transmitting said digital status signals to said station; and   means associated with said telephone station and responsive to said serial digital status signals for activating the indicating means.   
     
     
       19. In a multi-line key telephone system providing direct voice communication with selected telephone lines external to the system, the external lines being selectable by at least one telephone station, each station providing a talkpath and having line selecting keys and means for indicating the status of the selectable line: a voice line internal to the system, coupled to each of the respective external telephone lines;   controllable crosspoint switch means adapted for installation at a location remote from the telephone stations for selectably establishing, in response to activation of the telephone keys by the user, voice signal connections between selected voice lines and talkpaths associated with the selecting telephone stations;   means for impressing upon said voice lines signals representative of the status thereof, said status signals being distinct from voice signals carried by said talkpaths;   means responsive to said status signals for developing corresponding digital status signals;   means associated with the telephone station for developing at least one digital signal representing a line selected by activation of a line-selecting key of said station; and   data management means for controlling the flow of digital data to and from said station, including means for serially transmitting line-selecting data from said station to said controllable crosspoint switch means for operating the appropriate crosspoint switches in accordance with the line-selecting data.   
     
     
       20. The telephone system of claim 19, wherein: the status signal for a connected line is determined by an electrical condition on the talkpath associated with the selecting station, whereby the status signal appears on the selected line upon closure of the crosspoint switch.   
     
     
       21. In a multi-line key telephone system providing direct voice communication with selected telephone lines external to the system, the external lines being selectable by at least one telephone station, each station providing a talkpath and having line selecting keys and means for indicating the status of the selectable line: voice lines internal to the system;   a transformer for coupling each of the respective external telephone lines to one of said voice lines and providing direct current isolation between said external line and said voice line;   crosspoint switch means adapted for installation at a location remote from the telephone stations for selectably establishing, in response to actuation of the telephone keys by the user, a voice signal connection between a selected voice line and a talkpath associated with the selecting telephone station;   a second transformer for providing direct current isolation in the talkpath between each station and said crosspoint switch means;   means for impressing upon said voice signal connection, a direct current signal representative of the status of at least the connected voice line, said direct current signal being restricted to said connection between said transformers and thereby isolated from said external lines; and   means responsive to said direct current signal for activating the indicating means of each such telephone station to indicate the status of the lines.   
     
     
       22. The telephone system of claim 21, further comprising: means responsive to said direct current status signal for developing a corresponding encoded signal; and   a serial conductor for communicating said encoded signal to said telephone station, said station indicating means being responsive to such serially communicated encoded signal.